Which of the following identifies the most important reason why the percentage of deaths due to infectious diseases dropped from 1970 to 2015?
Group of answer choices

A. The number of people living in poverty fell as nations became increasingly more developed.

B. More people moved into urban areas, and fewer people remained in disease-prone rural areas.

C. More children were immunized against the major infectious diseases.

D. The use of pesticides became increasingly effective at killing biological threats.